Characteristics that materials for optical waveguides are required to have are less light absorption and low polarization dependency in the near infrared region used in the optical communications, refractive index-adjustability, excellent patterning capacity for waveguides, less increment of optical loss attributed to moisture absorption, and high productivity. Quartz-based materials hitherto have been used as materials for optical waveguides. The quartz-based materials show less light absorption in the near infrared region, but have a problem in poor productivity, since the manufacturing of optical waveguides from these materials requires a lot of steps which undesirably include a sintering step at high temperatures.
To overcome this problem, a variety of polymer materials have been developed. For example, JP-A-5-1148 (Patent Registration No. 2851019) discloses fluorinated polyimide usable as an optical material for optical waveguides. Fluorinated polyimide-based materials, however, have a problem in polarization dependency since fluorinated polyimide has many phenyl groups in the molecule, and thus has polarization dependency attributed to the orientation of the phenyl groups, although having less CH groups in the molecule and thus showing less light absorption in the near infrared region. Moreover, the use of the fluorinated polyimide-based materials for optical waveguides undesirably needs a baking step at a high temperature, which leads to cracking due to a stress attributed to the difference in linear expansion coefficient between a substrate and a film thereon, and the reactive ion etching is needed for patterning, which increases the number of manufacturing steps, resulting in poor productivity. Further disadvantages of fluorinated polymers:                bad adhesion properties (Substrate/Polymer) of fluorinated materials        especially polyimides: high thermal expansion coefficient        lower glass-temperature Tg (polymers tend to crystallize, when the fluorine content exceeds a certain amount)        
Japanese Patent Registration No. 3445485 discloses a thermooptic device comprising a specified silicone material. However, silicone-based materials also suffer from the following problem: A silicone-based material is cured by reacting the remaining hydroxyl groups or alkoxy groups, accompanied by the formation of water or alcohol. As a result, it becomes impossible to increase the thickness of the resulting film, which limits the kinds of devices obtained from such a material. Moreover, reactive ion etching is needed for patterning, which increases the number of manufacturing steps, resulting also in a poor productivity.
Further, organic/inorganic hybrid materials having organic reactive groups and siloxane backbones are reported as materials which show less light absorption in the near infrared region and less polarization dependency, and which can be patterned by photolithography and also form less by-products (cf. WO 01/04186 A1).
According to the materials disclosed in this publication, the hydroxyl groups of Ar2Si(OH)2 are reacted (alkoxylation) with the alkoxy groups of RSi(OR′)3 in the ratio 1:1, and the resultant resinous product is blended with a photopolymerization initiator to obtain a resin composition which can be patterned by photolithography. This material shows less polarization dependency, because, if phenyl groups are contained in the molecules of the material, such phenyl groups are not oriented on the straight chain. In addition, this material has more excellent properties compared to optical waveguide material, since by-products such as water, alcohol or the like are not formed when the organic reactive groups thereof are cured. However, this material still has problems in water- and moisture-absorption, because of residual alkoxy groups remaining after reaction of the hydroxyl groups of Ar2Si(OH)2 with the alkoxy groups of RSi(OR′)3 in a ratio 1:1.
As has been discussed above, there is no polymer material available that displays all the required properties in good balance in state of the present art.